Conventionally, attempts have been made to use a hybrid vehicle as a power supply system, for more effective use of hybrid vehicles. As an example, a hybrid vehicle having a dedicated inverter for converting a DC (Direct Current) voltage generated in the hybrid vehicle to a commercial AC voltage has been known.
Meanwhile Japanese Patent Laying-Open No. 04-295202 discloses an electric motor drive and power processing apparatus capable of generating an AC voltage and supplying the voltage to an external apparatus without necessitating a dedicated inverter. The electric motor drive and power processing apparatus includes a secondary battery, inverters IA and IB, three-phase AC motors MA and MB, and a control unit. Three-phase AC motors MA and MB respectively include three-phase windings CA and CB in a Y-configuration, and to neutral points NA and NB of three-phase windings CA and CB, an input/output port is connected through an EMI filter.
Inverters IA and IB are provided corresponding to three-phase AC motors MA and MB, respectively, and connected to three-phase windings CA and CB, respectively. Inverters IA and IB are connected parallel to the secondary battery.
In the electric motor drive and power processing apparatus, inverters IA and IB generate sinusoidal, regulated AC power at neutral points NA, NB, and the generated AC power can be output to an external apparatus connected to the input/output port.
In the electric motor drive and power processing apparatus disclosed in Japanese Patent Laying-Open No. 04-295202, however, it is impossible to generate the AC voltage across neutral points NA and NB while the three-phase AC motors MA and MB are driven. Here, assuming that the inverters generate the AC voltage across the neutral points while driving the motors, it follows that the voltage input to the inverters is used divided for driving the motors and for generating the AC voltage. Therefore, there might be a situation that the inverter driving the motor cannot secure one of or both of the voltages for driving the motors and for generating the AC voltage. As for the generation of AC voltage, voltage burden can be shared by the two inverters, and therefore, voltage burden on the inverters should desirably be varied in accordance with motor load.
In Japanese Patent Laying-Open No. 04-295202 described above, a specific method of feedback control for generating a desired AC voltage across neutral points NA and NB is not disclosed. In a hybrid vehicle requiring high reliability, feedback control of particularly high stability is desirable. It is also desirable to select an appropriate method of feedback control in consideration of voltage margin in each inverter and computational burden of the processing apparatus.
Further, in switching control of an inverter, generally, there is a dead time provided for preventing simultaneous turn-on of upper and lower arms, and this dead time causes waveform distortion in the waveform of AC voltage generated across the neutral points. Particularly in a large power inverter such as used for a hybrid vehicle, the dead time is often set longer, resulting in more serious waveform distortion in the AC voltage generated across the neutral points. In Japanese Patent Laying-Open No. 04-295202 described above, the waveform distortion in the AC voltage caused by the influence of inverter dead time is not at all discussed.